A new principle of discrimination between inrush current and internal short circuit of transformer based on fuzzy sets

A criterion of extracting the dead angle characteristic of the power transformer based on the wavelet is presented in the paper. Another criterion of extracting the symmetry feature of the internal fault current waveform based on an integral algorithm is also proposed. The fuzzy math models and the integral principle used to discriminate the inrush current and the fault current are developed in the paper based on these criteria. All the conclusions are verified by the EMTP and the electric power system simulation lab of NCEPU and proved to be highly accurate and fast